The present invention relates to generally a pressure responsive sequencing device for use in hydraulic actuating system and more particularly a pressure responsive sequencing device which may accomplish the sequential operations even in the meter-out flow control mode.
In general, the pressure responsive sequential control is possible only in a hydraulic system which may be maintained in the meter-in flow control mode over the whole operation of a primary actuating circuit, but it is very difficult to attain the pressure responsive sequential control in a hydraulic system which is switched to the meter-out flow control mode. The reason is that when the whole operation of the primary actuator circuit is controlled in the meter-in flow control mode, the supply pressure to the primary actuator circuit is suddenly increased when the operation of the primary actuator circuit has been accomplished so that when the set pressure of a sequencing valve inserted into a supply line to a secondary actuator circuit which is branched from the supply line from the primary actuator circuit is set slightly higher than the load pressure produced in the primary actuator circuit, the sequencing valve may be opened immediately when the operation of the primary actuator circuit has been accomplished whereby the so-called pressure responsive sequential control for starting the operation of the secondary actuator circuit may be attained. When the speed of the load is controlled in the hydraulic actuating system in such a way that the load which is at rest is accelerated to a predetermined speed, maintained at this speed for a predetermined time to accomplish a desired work, then decelerated and stopped, the meter-in control must be accomplished during the acceleration in which the direction of the load is positive, and when the direction of the load is reversed to negative and then the load is decelerated, the flow control must be switched to the meter-out control system. In such hydraulic control system, the supply pressure rises to the set pressure of the relief valve as soon as the hydraulic actuating system has been switched to the meter-out flow control. Therefore when the sequencing valve is inserted in the supply line to the secondary actuator circuit, it is immediately opened when the primary actuator circuit is changed to the meter-out flow control mode so that an erratic operation of the secondary actuator circuit may be started.